1. Field of the Invention
This invention relates generally to a disk used for magnetic recording in a disk drive and more specifically to an oriented magnetic medium on a non-metallic substrate.
2. Description of the Background Art
Disk drives using magnetic recording of digital information are used for most of the information storage in contemporary computer systems. Disk drives have at least one rotating disk with discrete concentric tracks of data. There is at least one recording head typically including a separate write element and read element for writing and reading the data on the tracks. The recording head is attached to a slider and the slider is attached to a suspension. The combination of the recording head, slider and suspension is called a head gimbal assembly. In addition, there is an actuator which positions the recording head over the specific track of interest. The actuator first rotates to seek the track of interest and after positioning the recording head over that track maintains the recording head in close registration to that track.
The disk in a disk drive includes a substrate and a magnetic layer on the substrate for magnetic recording. Substrates are typically either metal or glass. Metal substrates are typically made from an alloy of aluminum and magnesium. Glass substrates can be made with standard sodium borosilicate glass, harder grades of glass, or known glass composites. Substrates may also be made from silicon or a ceramic material. Silicon and ceramic disks offer many of the same technical advantages as glass but are generally more expensive. The magnetic layer is usually a cobalt based alloy suitable for magnetic recording. Disks generally have other layers in addition to the magnetic layer. There is usually a carbon based overcoat deposited on the magnetic layer for durability. Also there may be other layers disposed between the substrate and the,magnetic layer to promote better adhesion or to improve the magnetic properties of the recording layer. One or more underlayers deposited for the purpose of influencing the crystalline growth of the magnetic layer will be called herein a magnetic underlayer. The magnetic underlayer is generally itself non-magnetic and merely influences the properties of the magnetic recording layer.
When using metal substrates it is customary to electrolessly plate an underlayer of NiP from a solution. The NiP underlayer thus deposited generally has a thickness of several microns (typically 3-5 xcexcm) to cover some of the defects usually encountered in the substrate. A relatively thick layer of NiP is known to accept a mechanical texture. The composition of the NiP layer on a metal substrate using a deposition from solution is typically about 11% P by weight. This deposition method used with metal substrates produces the amorphous form of NiP. The crystalline form of NiP is magnetic and, if present, would degrade the magnetic recording properties of the disk.
Glass substrates have several advantages over metal substrates. Generally the surface of a glass substrate is smoother than the surface of a metal substrate. This is a significant advantage as the spacing between the disk and recording head must decrease as the areal density increases. A second advantage is that glass is a harder material than aluminum and therefore is more resistant to damage arising from inadvertent contact between the slider and the disk. A third advantage of using glass substrates is that glass substrates are stiffer than metal substrates which allows glass substrates to be used at higher rotation speeds. Another advantage of using glass for substrates is that glass has fewer detrimental effects during process temperature excursions compared with metal substrates. These advantages are generally known in the art.
For longitudinal media, orientation from crystallographic effects arises from constraining the c-axis of the magnetic film to lie in the plane of the magnetic layer. This magnetic orientation is normally isotropic within the plane of the magnetic recording layer. If, in addition, the magnetic layer is deposited on a surface which has been textured in a preferentially circumferential direction, then the magnetic orientation will also be preferentially circumferential for magnetic films of practical interest. In this case the orientation will no longer be isotropic within the plane of the magnetic recording layer. The orientation ratio (OR) refers to the ratio of the product of the remanent magnetization and the magnetic film thickness (Mrt) when measured in the circumferential direction relative to the Mrt in the radial direction. An OR of 1.0 means the Mrt is the same measured circumferentially and radially, and the media is said to be two dimensionally isotropic in the film plane. A disk with an OR greater than 1.0 generally has superior magnetic performance compared to isotropic disks. Circumferential in-plane orientation is commonly induced in recording layers on metal substrates by mechanically texturing the substrate or, more commonly, the NiP underlayer. Mechanical texturing on metal substrates leaves small elongated indentations or very small scratches in a generally circumferential direction.
Glass substrates are much more difficult to mechanically texture. Because glass is relatively brittle, texturing glass directly generally results in fracture pits, gouges, irregular scratches and other unacceptable artifacts. It is known to photolithographically produce grooves in a glass substrate, however this method is expensive and more difficult than mechanical texturing. Also the feature size available from a photolithographic process is generally larger than desired. As a consequence, glass substrates are rarely textured and the magnetic layers on glass substrates rarely have in-plane circumferential orientation.
There is needed an improved magnetic medium having orientation on a glass substrate and a practical method of making the medium with circumferential orientation.
An embodiment of this invention provides a disk which has an in-plane circumferential oriented recording layer on a glass or ceramic substrate. This disk includes a glass substrate and a NiP textured layer sputter deposited on the substrate. The NiP layer is textured in a substantially circumferential direction. The finished disk has a magnetic layer containing cobalt formed on the NiP textured layer, and an overcoat formed on the magnetic layer. The NiP textured layer is thin enough to preserve the smoothness of the substrate. The composition of Ni and P in the NiP layer is adjusted to avoid the ferromagnetic form of NiP.
Another embodiment of this invention is a disk drive, including a motor, a disk connected with the motor, an actuator, a head gimbal assembly attached to the actuator, and a recording head for magnetic recording on the disk. In this embodiment the disk has a glass substrate, a NiP textured layer deposited over the substrate, and the NiP textured layer is textured in a substantially circumferential direction. A disk drive containing the oriented disk shows improved magnetic performance.
The disk representing an embodiment of the invention combines the advantages of a rigid nonmetallic substrate along with the advantages of an oriented magnetic medium. Other aspects and advantages of the present invention will become apparent from the following detailed description along with the drawings, showing by way of examples the principles of the invention.